TW201538438A - Scale removal method and scale removal agent for steam generating facilities - Google Patents

Abstract

Provided are a scale removal method and a scale removal agent, both of which can efficiently remove scales adhered onto the inside of a boiler can or the like without causing the corrosion of a boiler in a steam generating facility even when used in an economically acceptable addition amount, particularly can efficiently remove scales adhered onto the inside of a boiler can even in a steam generating facility that can be operated with feed water containing iron at a high concentration. A scale removal method for removing scales adhered onto the inside of a system of a steam generating facility, wherein a polyacrylic acid having a weight average molecular weight of more than 20,000 and 170,000 or less and/or a salt thereof is added to feed water. When the feed water contains iron, a polymethacrylic acid having a weight average molecular weight of more than 1,000 and 100,000 or less and/or a salt thereof is also added in combination.

Description

Scale removal method for steam generating equipment and scale remover

The present invention relates to a scale removing method and a scale removing agent which can effectively remove scale adhering to a boiler tank or the like of a steam generating apparatus.

In recent years, in order to reduce energy costs and reduce the amount of water discharged to the outside of the system, the water system operating at a high concentration has increased. In such a water system, since scale components such as calcium, magnesium, and cerium oxide in water are still in a high concentration, scale formation of the components may cause a decrease in thermal efficiency of the heat exchanger or clogging.

In the boiler water system, scale components such as calcium, magnesium, strontium oxide, and iron that are carried into the boiler tank are adhered to scale due to the formation of scale on the heat transfer surface having a high heat load, thereby causing expansion and bending due to overheating of the steel material. The cause of the breakdown.

Since the adhesion of the scale on the heat transfer surface causes poor heat conduction, the thermal efficiency of the boiler is lowered, resulting in an increase in fuel cost. Therefore, in the boiler water system or the like, in order to prevent the adhesion of scale, calcium or magnesium which is a hardness component in the raw water is removed by a water softener, and it is softened and used as water supply.

By adding a scale inhibitor to the boiler water, it is possible to suppress the adhesion of a trace amount of a hardness component or a scale component such as cerium oxide in the feed water brought into the boiler tank to the system, and discharge the components to the body by discharging Water treatment methods outside the system.

The scale inhibitor refers to a substance that prevents the formation of scale by the hardness component brought into the water system. A polymer such as phosphate or sodium polyacrylate such as trisodium phosphate or sodium tripolyphosphate is used as a scale inhibitor.

When the scale prevention method is used, leakage of the hardness component which cannot be measured by the water supply system is generated, and scale is adhered to the boiler tank. At this time, the operation of the boiler is stopped, and the boiler water is discharged by full discharge, and chemical cleaning using the scale dissolution remover is performed. Patent Document 1 describes a scale removal method by chemical cleaning using a high concentration of a chelating agent such as ethylenediaminetetraacetic acid (EDTA) or an organic acid such as sulfamic acid.

In the scale removing method of Patent Document 1, there is a problem that the productivity is impaired due to the temporary stop of the boiler, and the cleaning cost is additionally generated.

Patent Document 2 proposes a method of removing scale without stopping the operation of the boiler. In the method of Patent Document 2, a specific chelating agent such as EDTA, nitrogen triacetic acid (NTA) or diethylenetriamine, and a specific dispersing agent such as polymaleic acid are added to the boiler tank to make the boiler The operation side removes scale.

The chelating agent used in the scale removing method of Patent Document 2 also acts on the iron chelating agent belonging to the base material of the boiler to cause corrosion.

Patent Document 3 proposes a method in which a chelating agent and an anticorrosive agent are used in combination. In the method of Patent Document 3, the chelating agent and the aldonic acid or a salt thereof are used to suppress corrosion while removing scale by a chelating agent.

In the scale removing method of Patent Document 3, there is a problem in that an anticorrosive agent is added depending on the amount of the chelating agent to be added, and the cost of the anticorrosive agent is additionally generated.

Patent Document 4 proposes a method of removing hardness scale without using a chelating agent. In the method of Patent Document 4, a water-soluble anionic vinyl having a molecular weight of from 500 to 50,000 in a range of from 500 to 50,000 is used, which comprises at least 30% by weight of a carboxyl chelate functional unit, a chelating value of at least 200 A composition comprising a mixture of a base polymer metal ion chelating agent and another water-soluble anionic vinyl polymer dispersant. According to Patent Document 4, when the hardness and iron are simultaneously introduced, the metal ion chelating agent and the dispersing agent are added at a high concentration, whereby the adhesion of the hardness scale or the removal effect of the adhered scale can be prevented.

However, in order to obtain the scale removing effect by the composition of Patent Document 4, an extremely large amount of the amount of the agent to be added is required and there is an economic problem. In the feed water with low hardness and high iron content in the feed water, the scale removal effect during operation decreases with time, and there is also a problem that sufficient removal effect cannot be obtained.

[Patent Document 1] Japanese Patent Laid-Open No. Hei 4-193971

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2000-154996

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2011-212591

[Patent Document 4] JP-A-63-65999

In view of the above, the present invention has been made in view of the fact that it is possible to provide a scale removing method and a scale removing agent which can effectively remove the scale adhering to the boiler tank or the like in an economically acceptable amount. . The present invention is to provide a scale removing method and a scale removing agent which can effectively remove scale adhering to a boiler tank in an apparatus which operates with a water supply containing a high concentration of iron.

As a result of intensive studies to solve the above problems, the present inventors have found that by using polyacrylic acid and/or a salt thereof having a specific molecular weight range, scale adhering to the system can be effectively removed with a small added concentration. As a result of further investigation, it has been found that when the liquid recovery is reused as the water supply, and the steel material is used for the highly corrosive energy saver, even if the feed water contains a high concentration of iron, the specific molecular weight range is used in combination. Polymethacrylic acid and/or its salt can not solve the above problems without reducing the scale removal efficiency.

The present invention is based on the following:

[1] A scale removing method for a steam generating apparatus, characterized in that in a scale removing method for removing scale adhering to a system of a steam generating apparatus, polyacrylic acid having a weight average molecular weight of more than 20,000 and not more than 170,000 and/or Salt is added to the water in the vapor generating device or to the feed water of the vapor generating device.

[2] The method for removing scale of a steam generating device according to [1], wherein the polyacrylic acid and/or a salt thereof is added to a concentration of the polyacrylic acid and/or a salt thereof in water in a vapor generating portion of the vapor generating device. It becomes 1~1,000mg/L.

[3] The scale removing method of the steam generating apparatus according to [1] or [2], wherein the water supply system of the steam generating apparatus contains iron, and further comprises polymethacrylic acid having a weight average molecular weight of more than 1,000 and less than 100,000 and/or Or a salt thereof is added to the water in the vapor generating device or the feed water of the vapor generating device.

[4] The method for removing scale of a steam generating device according to [3], wherein the polymethacrylic acid and/or a salt thereof is added to the polymethacrylic acid and/or the water in the vapor generating portion of the vapor generating device. The concentration of the salt is 1 to 1,000 mg/L.

[5] The method for removing scale of a steam generating device according to [3] or [4], which comprises adding polyacrylic acid and/or a salt thereof and polymethacrylic acid and/or a salt thereof to cause a vapor generating portion of the steam generating device The weight concentration ratio of polyacrylic acid and/or a salt thereof to polymethacrylic acid and/or a salt thereof in the water is 1:100 to 100:1.

[6] A scale removing agent for a steam generating device, characterized in that a scale removing agent for removing scale adhering to a system of a steam generating device comprises polyacrylic acid having a weight average molecular weight of more than 20,000 and 170,000 or less and/or The salt and polymethacrylic acid and/or a salt thereof having a weight average molecular weight of more than 1,000 and 100,000 or less.

[7] A scale removing agent for a steam generating device such as [6], The polyacrylic acid and/or a salt thereof, and the above polymethacrylic acid and/or a salt thereof are contained in a weight ratio of 1:100 to 100:1.

According to the present invention, it is possible to effectively remove scale adhering to the system in the operation of the steam generating device without using a chelating agent, without corroding the system, and with a small amount of the agent; and, even if there is a high concentration of iron in the feed water At the same time, a high scale removal effect can still be obtained.

1‧‧‧Sink

2‧‧‧Boiler cans

3‧‧‧Reservation tank

4‧‧‧Supply sink

5‧‧‧Vapor use place

11‧‧‧Water supply pipeline

12‧‧‧Vapor pipeline

13‧‧‧Circular pipeline

14‧‧‧Rehydration pipeline

15‧‧‧Supply water pipeline

16‧‧‧Alkaline agent

17‧‧‧scale remover

18‧‧‧Drainage

Fig. 1 is a system diagram showing an embodiment of a steam generating apparatus for carrying out the present invention.

Hereinafter, embodiments of the present invention will be described in detail.

[Method of removing scale from steam generating equipment]

In the scale removing method of the steam generating apparatus of the present invention, in the steam generating apparatus, the polyacrylic acid having a weight average molecular weight of more than 20,000 and 170,000 or less is applied to the scale adhered to the system such as the steam generating portion of the boiler can. Or a salt thereof (hereinafter referred to as "polyacrylic acid (salt)") is added to the water in the vapor generating device or the feed water of the vapor generating device. When the feed water of the steam generating apparatus contains iron, it is preferred to use together a polymethacrylic acid having a weight average molecular weight of more than 1,000 and less than 100,000. Acid and/or its salt (hereinafter referred to as "polymethacrylic acid (salt)").

Fig. 1 is a system diagram showing an embodiment of a steam generating apparatus for carrying out the present invention, wherein 1 is a water supply tank, 2 is a boiler tank (a steam generating unit), 3 is a double water tank, 4 is a replenishing water tank, and 5 is a steam. Use place. The water supply system in the water supply tank 1 is sent from the water supply line 11 to the boiler tank 2. The steam generated in the boiler tank 2 is sent from the steam line 12 to the steam use place 5, and the re-water system is circulated to the water supply tank 1 through the circulation line 13, the double water tank 3, and the rehydration line 14.

In the water supply tank 1, the makeup water in the supply water tank 4 is supplied from the makeup water line 15, while the alkali agent is added from the alkali agent addition line 16, and the scale remover is added from the scale remover line 17. From the boiler tank 2, the drain is discharged from the discharge line 18.

In Fig. 1, a scale removing agent containing polyacrylic acid (salt) or polyacrylic acid (salt) and polymethacrylic acid (salt) is added to the feed water of the water supply tank 1. The scale remover may be added to the supply water tank 4, to the feed line of the double water tank 3 or each water system, or to two or more parts. When polyacrylic acid (salt) and polymethacrylic acid (salt) are used together, these may be added to each part or may be added to the same part. When it is added to the same site, polyacrylic acid (salt) and polymethacrylic acid (salt) may be previously mixed and added, or may be added individually. The same applies to other optional components described later.

Fig. 1 shows a circulating steam generating apparatus, but the present invention is not limited to the circulating type, and is applicable to a through-flow type or other steam generating apparatus.

As the feed water of the steam generating device, raw water may be used for treatment by a reverse osmosis membrane, raw water by a softening treatment, raw water by an ion exchange treatment or the like.

The operating conditions of the steam generating apparatus are not particularly limited, and the operating pressure is preferably 0.2 to 4 MPa, more preferably 0.2 to 3 MPa. When it is less than 0.2 MPa, sufficient scale removal effect cannot be obtained. When the pressure is higher than 4 MPa, polymers such as polyacrylic acid (salt) and polymethacrylic acid (salt) are affected by thermal decomposition, and the scale removal effect is lowered.

In the method for removing scale of the steam generating apparatus of the present invention, polyacrylic acid (salt) used as a scale removing component, polymethacrylic acid (salt) used in combination with polyacrylic acid (salt), and the like may be used. The other optional ingredients used in combination are explained.

<polyacrylic acid (salt)>

The polyacrylic acid is not particularly limited, and those satisfying the weight average molecular weight described later can be used. Examples of the polyacrylate include a sodium salt or a potassium salt of the above polyacrylic acid. The polyacrylate is formed by adding an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, an alkali metal carbonate such as sodium carbonate or potassium carbonate, or the like to the polyacrylic acid.

The polyacrylic acid used in the present invention has a weight average molecular weight of more than 20,000 and 170,000 or less, preferably more than 50,000 and 120,000 or less.

When the weight average molecular weight of polyacrylic acid is less than 20,000, sufficient scale removal effect cannot be obtained. Even the weight average of polyacrylic acid The molecular weight exceeds 170,000 and the scale removal effect is also reduced.

In the case of the polyacrylate, the weight average molecular weight of the polyacrylic acid as a matrix of the polyacrylate may be as long as the above conditions are satisfied.

The amount of the polyacrylic acid (salt) to be added is preferably such that the water in the steam generating portion of the steam generating device, that is, the concentration in the boiler water is 1 to 1,000 mg/L, particularly preferably 10 to 500 mg/L.

When the concentration of the polyacrylic acid (salt) in the boiler water is at least the above lower limit, the scale removal effect is easily exhibited, and by taking the above upper limit or less, the trouble of the drainage treatment due to the increase in COD can be prevented, and the effect of the cost can be further improved. .

Therefore, the polyacrylic acid (salt) is added to the water of each part in accordance with the concentration ratio of the vapor generating apparatus, and the concentration in the boiler water is in the above range.

The polyacrylic acid (salt) is preferably added using deionized water in an aqueous solution having a concentration of 0.1 to 30% by weight, particularly 0.5 to 10% by weight.

<polymethacrylic acid (salt)>

When the feed water of the steam generating apparatus contains iron, it is preferred to use polymethacrylic acid (salt) in combination with the above polyacrylic acid (salt).

In the case of iron in water, in general, water-insoluble substances such as iron hydroxide or iron oxide are present in a suspended state in the feed water, and the water-soluble substance is dissolved in water, dissociated, and exists as iron ions.

Both the suspensor and the solute are contained, especially when the iron contains more than 0.3 mg/L of iron, for example, at a high concentration of 0.4 to 5.0 mg/L. Preferably, polymethacrylic acid (salt) is used in combination with polyacrylic acid (salt).

The polymethacrylic acid is not particularly limited, and those satisfying the following weight average molecular weight are preferably used. The polymethacrylate may, for example, be a sodium salt or a potassium salt of the above polymethacrylic acid. The polymethacrylate can be produced by adding an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, an alkali metal carbonate such as sodium carbonate or potassium carbonate, or the like together with polymethacrylic acid.

The polymethacrylic acid used in the present invention preferably has a weight average molecular weight of 1,000 or more and 100,000 or less, more preferably 5,000 or more and 60,000 or less.

When the weight average molecular weight of polymethacrylic acid is less than 1,000, a sufficient iron scale preventing effect cannot be obtained; when the weight average molecular weight of polymethacrylic acid exceeds 100,000, the effect is lowered.

In the case of the polymethacrylate, the weight average molecular weight of the polymethacrylic acid as a matrix of the polymethacrylate may be as long as the above conditions are satisfied.

The amount of the polymethacrylic acid (salt) to be added is preferably such that the water in the steam generating portion of the steam generating device, that is, the concentration in the boiler water is 1 to 1,000 mg/L, particularly 10 to 500 mg/L.

When the concentration of the polymethacrylic acid (salt) in the boiler water is at least the above lower limit, the iron scale prevention effect can be exhibited, and the scale removal effect by the polyacrylic acid (salt) can be easily maintained. By taking the above upper limit, it is possible to prevent the trouble of drainage treatment caused by an increase in COD, and at the same time Make the effect of the response cost better.

Therefore, the polymethacrylic acid (salt) is added to the water of each part in accordance with the concentration ratio of the vapor generating apparatus, and the concentration in the boiler water is in the above range.

In order to fully obtain and use the synergistic scale removal effect produced by polyacrylic acid (salt) and polymethacrylic acid (salt), polyacrylic acid (salt) and polymethacrylic acid (salt) are made into polyacrylic acid in the concentration of boiler water ( Salt): Polymethacrylic acid (salt) = 1:100~100:1, especially 1:50~10:1 by weight.

The polymethacrylic acid (salt) is preferably added in an aqueous solution having a concentration of 0.1 to 30% by weight, particularly 0.5 to 20% by weight, prepared by using deionized water.

<arbitrarily added ingredients>

In the present invention, an effective amount of various additive components such as a pH adjuster, an oxygen scavenger, an anticorrosive agent, and a scale dispersion may be added to any portion of the system of the vapor generating device as needed within the scope of the present invention. Agents, etc. These additional components may be used alone or in combination of two or more.

The pH of the boiler water is preferably adjusted to 11.0 or more, and is preferably adjusted to 12.0 or less based on the viewpoint of corrosion prevention in the boiler tank or in the steam generating equipment system. As a method of adjusting the pH of the boiler water to 11.0 or more, a method of adding an alkali agent and a method of adjusting the amount of discharge and/or the amount of water supplied to adjust the concentration ratio may be mentioned. Among them, a method of adding an alkali agent is suitable from the viewpoint of ease of pH adjustment.

Examples of the alkaline agent used for pH adjustment include an alkali metal hydroxide, an alkali metal carbonate, an alkali metal phosphate, a neutralized amine, and the like.

Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, and lithium hydroxide; examples of the alkali metal carbonate include sodium carbonate and potassium carbonate; and examples of the alkali metal phosphate include phosphoric acid Sodium, sodium hydrogen phosphate, and the like.

The neutralizing amine may, for example, be monoethanolamine, cyclohexylamine, morpholine, diethylethanolamine, monoisopropanolamine, 3-methoxypropylamine or 2-amino-2-methyl-1-propene. Alcohol, etc.

In the alkaline agent, the neutralized amine is transferred to the vapor rehydration system, and when added at a high concentration, the vapor or the rehydration water may be odorized, or the pH of the vapor rehydration system may be excessively increased. When the copper material is used in the system, The possibility of causing corrosion. Therefore, as the alkali agent, an alkali metal hydroxide, an alkali metal carbonate or an alkali metal phosphate is preferable, and sodium hydroxide, potassium hydroxide, sodium carbonate or the like is more preferable from the viewpoint of economy.

These alkaline agents may be used alone or in combination of two or more.

The alkali agent is preferably added to the make-up water or the feed water in the same manner as the scale remover. When the steam generating device is of a circulating type, it can also be added to the reconstituted water.

In order to supply an appropriate amount of an alkali agent, the steam generating apparatus of the present invention preferably has a pH measuring means on the upstream side and/or the downstream side of the boiler tank.

Examples of the oxygen scavenger include N-aminoheterocyclic compounds such as various hydroxylamines such as hydrazine, diamine urea, and diethylhydroxylamine, 1-aminopyrrolidine or 1-amino-4-methylpiperazine. , hydroquinone, hydrolyzed or condensed Ning (acid) and its salts, erythorbic acid or ascorbic acid and its salts, aldonic acid and its salts such as gluconic acid or α-glucoheptanoic acid, sugars such as glucose (monosaccharides, polysaccharides), sulfurous acid Or a sulfurous acid-based substance such as metabisulfuric acid or the like and a salt thereof. These may be used alone or in combination of two or more.

Examples of the anticorrosive agent include succinic acid, a polyvalent carboxylic acid such as citric acid or malic acid, an oxycarboxylic acid, a salt thereof, and the like. These may be used alone or in combination of two or more.

[scale remover for steam generating equipment]

The scale removing agent of the vapor generating apparatus of the present invention comprises polyacrylic acid (salt) having a weight average molecular weight of more than 20,000 and 170,000 or less, preferably more than 50,000 and 120,000 or less, and a weight average molecular weight of more than 1,000 and 100,000 or less. Preferably, it is characterized by more than 5,000 and less than 60,000 polymethacrylic acid (salt), preferably polyacrylic acid (salt): polymethacrylic acid (salt) = 1:100 to 100:1, more preferably The weight ratio of 1:50 to 10:1 includes polyacrylic acid (salt) and polymethacrylic acid (salt).

The scale remover of the present invention may also contain various water treatment agent components including the above-mentioned pH adjuster, oxygen scavenger, anticorrosive agent, scale dispersant, etc., within the range not impairing the object of the present invention.

The scale removing agent of the present invention may be a mixture of polyacrylic acid (salt) and polymethacrylic acid (salt), or may be an individual supplier.

For example, as described above, the polyacrylic acid (salt) is usually dissolved in deionized water at a concentration of 0.1 to 30% by weight, particularly 0.5 to 15% by weight. use. Further, polymethacrylic acid (salt) is usually dissolved in deionized water and used in an aqueous solution having a concentration of 0.1 to 30% by weight, particularly 0.5 to 20% by weight.

[Examples]

The present invention will be more specifically described by the following examples and comparative examples, but the invention is not limited by the examples.

In the following examples and comparative examples, in the preparation of the synthetic water used as the feed water, CaCl ₂ was used for the Ca hardness, MgCl ₂ was used for the Mg hardness, Na ₂ SiO ₃ was used for the lanthanum oxide, and FeCl ₂ was used for the Fe system.

[Test Example I: Examples I-1 to 6, Comparative Examples I-1 to 3]

Using the following test apparatus and feed water, the following scale removal test was carried out under the following conditions to evaluate the scale removal effect of polyacrylic acid and polymaleic acid.

<test device>

Stainless steel test boiler (water retention 5L)

<water supply>

Synthetic water A: Synthetic water with Ca hardness of 20 mg CaCO ₃ /L, Mg hardness of 10 mg CaCO ₃ /L, cerium oxide concentration of 15 mg/L, and sodium carbonate concentration of 30 mg/L

Synthetic water B: cerium oxide concentration 15 mg / L, polyacrylic acid or polymaleic acid concentration 10 mg / L, sodium carbonate, weight average molecular weight shown in Table 1 Synthetic water with a concentration of 32mg/L

<Test conditions>

Feed water temperature: 40 ° C

Operating pressure: 2.0MPa

Water supply: 10L/h

Concentration ratio: 10 times

Boiler water pH: 11.4

<scale removal test>

Weigh the heat pipe (made of steel; surface area 200cm ² × 3) and record it, then insert it into the stainless steel test boiler.

A filter screen with a diameter of 20 mm and 60 mesh is provided for the discharge line.

While supplying the synthetic water A to the stainless steel test boiler, the pressure was adjusted to 2.0 MPa, the evaporation amount was 9.0 L/h, the discharge amount was 1.0 L/h, and the concentration ratio was 10 times, and the operation was performed for 24 hours. After the operation, the heat pipe to which the scale is attached is taken out and weighed to calculate the scale adhesion amount. Thereafter, the heat transfer tube was again inserted into a stainless steel test boiler, and the synthetic water B was operated under the same operating conditions for 3 days to carry out a scale removal step.

After the scale removal operation, the heat transfer tube was taken out in the same manner and weighed, and the scale adhesion amount was calculated, and the scale removal rate was calculated from the amount of scale adhesion before and after the scale removal step.

Observe the filter after the test, and confirm that there is a filter screen. The presence or absence of sputum attachments.

The results are shown in Table 1.

<inspection>

As is clear from Table 1, the weight average molecular weight of the polyacrylic acid is 20,000 or less, and the scale removal rate is low. When the amount exceeds 20,000 and is 170,000 or less, the scale removal rate is improved, and when the amount is more than 50,000 and 120,000 or less, the scale removal effect is high.

On the other hand, although the polymaleic acid showed a certain degree of scale removal effect, the discharge screen confirmed that there was a sticky deposit, and most of the filter was covered to be in a state immediately before the blockage. It is presumed that this is due to the gelation of the hardness component reacted with polymaleic acid.

[Test Example II: Examples II-1 to 6 and Comparative Examples II-1 to 11]

Using the following test apparatus and feed water, the following scale removal test was carried out under the following conditions to evaluate the effect of the combined use of the weight average molecular weight of polyacrylic acid and polymethacrylic acid on the scale removal effect.

<test device>

Stainless steel test boiler (water retention 5L)

<water supply>

Synthetic water C: Synthetic water with Ca hardness of 40 mg CaCO ₃ /L, Mg hardness of 20 mg CaCO ₃ /L, cerium oxide concentration of 30 mg/L, sodium carbonate concentration of 30 mg/L, and Fe concentration of 1 mg/L

Synthetic water D: a cerium oxide concentration of 30 mg/L, a polyacrylic acid concentration of 5 mg/L as a weight average molecular weight described in Table 2 of the drug 1, a concentration of 5 mg/L as shown in Table 2 of the drug 2, and a Fe concentration of 1 mg/L. Synthetic water having a sodium carbonate concentration of 32 mg/L (except that the drug 1 and the drug 2 were not added in Comparative Example II-1, and the drug 2 was not added in Comparative Example II-2 to 8)

<Test conditions>

Feed water temperature: 40 ° C

Operating pressure: 0.7MPa

Water supply: 13L/h

Concentration ratio: 10 times

Boiler water pH: 11.5

<scale removal test>

Weigh the heat pipe (made of steel; surface area 200cm ² × 3) and record it, then insert it into the stainless steel test boiler.

While supplying the synthetic water C to the stainless steel test boiler, the pressure was adjusted to 0.7 MPa, the evaporation amount was 11.7 L/h, the discharge amount was 1.3 L/h, and the concentration ratio was 10 times, and the operation was carried out for 21 hours. After the operation, the heat pipe to which the scale is attached is taken out and weighed to calculate the scale adhesion amount. Thereafter, the heat transfer tube was again inserted into a stainless steel test boiler, and the test was carried out under the same operating conditions using synthetic water D to carry out a scale removal step. After the operation, the heat transfer tubes were taken out in the same manner and weighed, and the scale adhesion amount was calculated, and the amount of scale removal was calculated from the scale adhesion scale before and after the scale removal step. The amount of scale removal was measured by taking out the heat transfer tube every three days and re-inserting it, and performing a scale removal step for 9 days in total, and calculating the scale removal rate after the scale removal step of 9 days (relative to the start of the scale removal step) The proportion of the scale that can be removed within 9 days of the attached scale).

The results are shown in Table 2.

<inspection>

The following is known from Table 2.

In Comparative Examples II-2 to II-8, the amount of scale removal continued to decrease with the number of days passed. This system further adheres to the iron scale on the adhered scale, and the polyacrylic acid is treated separately, so that the scale removal effect cannot be maintained. Therefore.

Comparative Example II-11 used two kinds of polymers in combination, but the removal effect was low. The same removal effect was also similar in Comparative Examples II-9, II-10.

On the other hand, in Examples II-1 to II-6, scales were removed at a constant speed even after one day passed. This system can prevent the adhesion of iron scale by using polymethacrylic acid in combination, and at the same time, the scale removal effect by the polyacrylic acid having a higher weight average molecular weight can be kept constant.

[Test Example III: Examples III-1 to 6 and Comparative Examples III-1 to 4]

In Test Example II, a steel test piece (SPCC; 15 × 50 × 10 mm; #400 polishing) was placed in a can of the test boiler, and supplied under the same conditions as in Test Example II to be in the boiler can shown in Table 3. The method of concentration includes the synthetic water of the agent shown in Table 3 for the corrosive confirmation test. The pH in the boiler tank was adjusted to 11.3.

After the test, the test piece was taken out and subjected to a rust removal treatment, and the corrosion rate was determined according to the following calculation formula (1).

Corrosion rate (mdd) = corrosion loss of the test piece (mg) / (surface area of the test piece (dm ² ) × test time (day)) (1)

The results are shown in Table 3.

From the results of Table 3, it was found that the treatment with polyacrylic acid and polymethacrylic acid was particularly slow in corrosion rate and corrosion inhibiting effect compared to the treatment using a chelating agent such as EDTA or NTA.

The present invention has been described in detail with reference to the specific embodiments thereof, and it is understood by those of ordinary skill in the art that various modifications can be made without departing from the spirit and scope of the invention.

The present application is based on Japanese Patent Application No. 2014-025459, filed on Jan.

1‧‧‧Sink

2‧‧‧Boiler cans

3‧‧‧Reservation tank

4‧‧‧Supply sink

5‧‧‧Vapor use place

11‧‧‧Water supply pipeline

12‧‧‧Vapor pipeline

13‧‧‧Circular pipeline

14‧‧‧Rehydration pipeline

15‧‧‧Supply water pipeline

16‧‧‧Alkaline agent

17‧‧‧scale remover

18‧‧‧Drainage

Claims (7)

A method for removing scale of a steam generating device, characterized in that in a scale removing method for removing scale adhering to a system of a steam generating device, polyacrylic acid and/or a salt thereof having a weight average molecular weight of more than 20,000 and not more than 170,000 is added to The vapor in the steam generating device or the feed water of the vapor generating device. The method for removing scale of a steam generating device according to claim 1, wherein the polyacrylic acid and/or a salt thereof is added so that the concentration of the polyacrylic acid and/or a salt thereof in the water generating portion of the vapor generating device becomes 1~ 1,000mg/L. The scale removing method of the steam generating apparatus of claim 1 or 2, wherein the water supply system of the steam generating apparatus contains iron, and further adding polymethacrylic acid and/or a salt thereof having a weight average molecular weight of more than 1,000 and less than 100,000 to The vapor in the steam generating device or the feed water of the vapor generating device. The method for removing scale of a steam generating device according to claim 3, wherein the polymethacrylic acid and/or a salt thereof is added to make the polymethacrylic acid and/or a salt thereof in the water of the vapor generating portion of the vapor generating device The concentration is 1 to 1,000 mg/L. A method for removing scale of a steam generating apparatus according to claim 3 or 4, wherein polyacrylic acid and/or a salt thereof and polymethacrylic acid and/or a salt thereof are added to make the polyacrylic acid in the water of the vapor generating portion of the vapor generating device And/or the ratio by weight of its salt to polymethacrylic acid and/or its salt 1:100~100:1. A scale removing agent for a steam generating device, characterized in that a scale removing agent for removing scale adhering to a system of a steam generating device comprises polyacrylic acid and/or a salt thereof having a weight average molecular weight of more than 20,000 and not more than 170,000, and Polymethacrylic acid and/or a salt thereof having a weight average molecular weight of more than 1,000 and 100,000 or less. The scale removing agent of the vapor generating apparatus of claim 6, wherein the polyacrylic acid and/or a salt thereof, and the polymethacrylic acid and/or a salt thereof are contained in a weight ratio of 1:100 to 100:1.